1. Field of the Invention
This invention relates to devices for the transmission of signals for initiation of detonations, and more particularly to signal transmission relay and initiation devices for delayed transmission of pyrotechnic or detonation initiation signals.
2. Related Art
The prior art is well aware of the use of signal transmission lines, such as signal transmission tubes, to transfer initiation signals to initiate pyrotechnic or detonation events and the use of pyrotechnic delays to help time the occurrence of such events.
Signal transmission lines, i.e., fuses, of the type disclosed in U.S. Pat. No. 3,590,739 issued Jul. 6, 1971 to P. A. Persson, U.S. Pat. No. 4,328,753, issued May 11, 1982 to L. Kristensen et al and U.S. Pat. No. 4,607,573 issued Aug. 26, 1986 to G. R. Thureson et al comprise signal transmission tubes and are commonly referred to as "shock tubes". Shock tubes comprise an elongated hollow tube made of one or more layers of synthetic organic polymeric material(s) (plastics) containing on the interior wall thereof a thin coating of reactive material such as a pulverulent mixture of a high brisance explosive and reducing agent, for example, a mixture of PETN, HMX, RMX or the like, and aluminum powder. The tube is hollow, providing an open channel or bore extending the length of the tube. When the reactive material is ignited, as by a spark igniter or a detonator cap used as a signal-transmitter, or by any other suitable means, ignition of the reactive material propagates an initiation signal through the open bore of the tube.
U.S. Pat. No. 4,757,764, issued Jul. 19, 1988 to G. R. Thureson et al discloses low velocity signal transmission ("LVST") tubes comprising plastic tubes as described above except that the reactive material is a low velocity deflagrating material, e.g., manganese/potassium perchlorate, silicon/red lead, zirconium/ferric oxide, etc., instead of an explosive powder of high brisance. The deflagrating material provides a speed of transmission of the initiation signal propagated through the tube of about one-third that of shock tubes.
The connection of shock tube initiator devices in series or other sequence is shown, for example, in R. W. Spraggs U.S. Pat. No. 3,987,732.
The use of static electricity dissipation means, such as isolation members, in non-electric detonator caps which are to be assembled to fuses of a type capable of transmitting a static electric charge, e.g., a shock tube or LVST tube, is known in the art, as shown in U.S. Pat. No. 3,981,240, issued Sept. 21, 1976 to E. L. Gladden.
U.S. Pat. No. 4,911,076 to Rowe, dated Mar. 27, 1990, discloses a signal delay device comprising a delay detonator cap connected to a pair of shock tubes. Portions of both shock tubes are disposed externally of the cap in close proximity to the closed, output end of the cap, i.e., the active end of the cap. One end of each shock tube is disposed in the detonator cap shell in signal transfer relation to the delay element. An incoming signal in either shock tube can initiate the delay element, but the shock tubes have sealed ends so that one shock tube cannot fire the other and the burning of the delay element will not initiate a signal in the as yet un-fired shock tube, i.e., the output shock tube. Accordingly, an incoming signal from either shock tube will ignite the delay element, and after the predetermined delay, detonation of the charge in the device will initiate a signal in the other shock tube, through the wall thereof, exteriorly of the cap. Thus, the device provides a delay in the transfer of a signal between the two shock tubes.